The present invention relates to a cylinder head gasket which is placed between two members such as a cylinder head and a cylinder block for an engine with a cylinder liner. More specifically, a cylinder head gasket is able to absorb a level difference or gap between the cylinder head and cylinder case.
The cylinder head gasket is fastened by head bolts in the state of being placed between engine members such as the cylinder head and the cylinder block (cylinder body) of an automobile engine in order to seal fluid, such as combustion gas, oil, coolant water and so on.
On the other hand, recently, with improved fuel consumption and stronger antipollution measures, the automobile engine has been reduced in size and weight. The development of this compact engine focuses on low-fuel consumption, and fuel consumption has been improved by reducing the friction resistance of the piston ring and cylinder.
As one measure, an engine with a cylinder liner having a cylinder-bore shape and being made of special cast iron which is excellent in abrasion resistance, seize resistance, heat resistance, and strength, is used. The cylinder liner is fit into an aluminum alloy cylinder case and forms a cylinder block.
There are a dry liner and a wet liner in this cylinder liner. In the case wherein the cylinder liner is the dry liner which does not contact the water jacket, there may be a case wherein the level difference or gap is generated between the upper face of the flange of the cylinder liner and the deck face of the cylinder block, i.e., in the borderline portion between the cylinder liner and the cylinder block.
In the case wherein the level difference or gap is formed, when the gap between the engine members is expanded and reduced due to vibration during the engine operation, large surface pressure is locally generated in the portion of the gasket wherein the corner portion of the level difference abuts. Since the above-mentioned surface pressure repeatedly acts on the bottom of the portion with a bead which seals the adjacent water hole of the water jacket, the bead for sealing the water hole vibrates, and repeatedly hits the engine members. Accordingly, this may cause damage in such a way as to make a hole in the contact face of the bead for sealing the water hole of the engine members. If this fretting occurs, sealing performance deteriorates, and creep relaxation of a seal portion around the water jacket occurs, so that durability deteriorates.
In relation to a cylinder head gasket for an engine with a cylinder liner, a metal gasket which is able to reduce the deformation of a combustion hole and prevents the bead from fatigue breakdown, is proposed (for example, refer to the Japanese Patent Publication 1). The purposes of the metal gasket are that, even if there is a level difference or gap at the borderline portion between the upper face of the flange of the cylinder liner and the deck face of the cylinder block, the gasket can absorb the level difference and carry out an excellent sealing performance. For this purpose, the metal gasket includes inner beads formed by half beads around the combustion holes of a first metal plate and a second metal plate respectively; and outer beads formed by full beads outside the inner beads. These beads are formed in a projection on the inside, and two sheets of the secondary plates with a level difference portion which can achieve a stopper effect in the corresponding position between the inner beads and the outer beads, are provided between the first metal plate and the second metal plate.
The metal gasket can obtain an excellent sealing performance by forming three-stage seal lines by a primary seal of the tip of a first inner bead; a secondary seal between the inner bead and the outer bead; and a tertiary seal of the outside base portion of the outer bead. Also, the level difference portion of the secondary plates produces the stopper effect of the secondary seal, and prevents the fatigue breakdown of both beads.
As a metal gasket with a similar structure, a metal gasket wherein the first metal plate and the second metal plate are provided with the full beads around the combustion hole respectively, is proposed (for example, refer to Japanese Patent Publication 2). These beads project to orient inwardly, and the secondary plates are provided between the first metal plate and the second metal plate, and between the inner bead and the outer bead.
In the metal gasket, two-stage seal lines are formed by the primary seal and the secondary seal at the inside and the outside of the bottom portion of the full beads.
In the above-mentioned two types of metal gaskets, the beads are arranged to cross the borderline (level difference) between the flange of the cylinder liner and the cylinder case, so that even if there is a level difference on the deck face of the cylinder, the gasket can follow. As a result, the sealing can be carried out excellently, and the deformation of the cylinder liner can be also reduced.
However, in the metal gasket with the above-mentioned structure, even if the beads cross the level difference of the borderline, the vibration of the engine member is applied to the bottom portion of the outer circumferential side of the beads, so that fretting might occur. Moreover, in the portion facing the combustion chamber, since the end of each constitution plate of the gasket is exposed to the combustion chamber, the combustion gas in the combustion chamber enters between the first metal plate and the second metal plate. As a result, all of the first metal plate, the second metal plate, and the secondary plates contact with high-temperature combustion gas.
Therefore, there is a possibility of producing a combustion gas leak between the above-mentioned metal plates. Also, because all of the metal plates are required to be formed by metal with heat resistance and corrosion resistance relative to the high-temperature combustion gas, the metal gasket with the metal plates with several properties cannot be combined for applying respective properties.
Patent Publication 1: Japanese Patent Publication No. TOKKAI H10-267131
Patent Publication 2: Japanese Patent Publication No. TOKKAI H11-241769
The present invention is made in order to solve the above-mentioned problem, and the purpose of the present invention is to provide a cylinder head gasket used for an engine with a cylinder liner. The cylinder head gasket can block the combustion gas from the folded portion, and be combined with the metal plates with several properties in such a way that the combustion gas does not contact the metal plates except for the metal plate with the folded portion, so that the cylinder head gasket can improve the sealing performance. Also, the cylinder head gasket can absorb the level difference of the borderline portion between the cylinder liner and the cylinder case, and the vibration of the engine members can be absorbed by a damper bead, so that fretting can be controlled. Accordingly, the cylinder head gasket can maintain high sealing performance with high durability.
Further objects and advantages of the invention will be apparent from the following description of the invention.